1. Java Packages
B.Ramamurthy
11/11/2018
B.Ramamurthy

2. Topics for Discussion Keyword package Packaging a set of classes
CLASSPATH reference to a package
Example
Creating a Java Archive (jar)
Using a jar file
Summary
11/11/2018
B.Ramamurthy

3. Keyword “package”
Package construct is used to package a set of related class.
You will find many examples in Java API: java.util package, java.lang package etc.
To include a class into a package: add a statement
package package_name;
before the class header.
11/11/2018
B.Ramamurthy

4. “package” Definition
1. Add “package package_name” to all the java source files that contains class definition to be included in the package.
2. Create a directory “package_name”
3. Compile and place the class files in a directory “package_name”
11/11/2018
B.Ramamurthy

5. “package” Usage
1. Update your CLASSPATH environment variable to include the path where the directory is located.
2. Make sure the update is effective by executing “source .cshrc”
3. Include import package_name.*; in the application/applets where you want to use these classes.
11/11/2018
B.Ramamurthy

6. Example
Look at ch17, fig17_04
The application is in CreateSequentialFile.java.
The classes it uses are BankU.javaI and BankAccountRecord.java
Lets create a package ch17 out of these two classes.
Create a directory ch17 anywhere you want. Move BankUI.java and BanAccountRecord.java into this directory.
Add “package ch17; at the top of the two files. Remove any other reference to packages.
11/11/2018
B.Ramamurthy

7. Example (contd.)
Compile the files BankUI.java and BankAccountRecord.java
Update .cshrc to include the path to the parent directory of ch17.
“source .cshrc”
Update CreateSequentialFile.java to import classes from ch17;
“import ch17.*;”
Compile and execute.
11/11/2018
B.Ramamurthy

8. Archiving the Package
Often once the classes are related by package, and after they are tested well, they are compressed using a “jar” tool to provide an easy way to transport the package as one.
Command (See man jar)
jar cf jar_file_name classes to be archived
Examples:
jar ch17.jar BankUI.class Record.class BankAccountRecord.class
11/11/2018
B.Ramamurthy

9. Including “jar” file in CLASSPATH
When a package is in the form of a .jar file, you need actually include the jar file in the CLASSPATH.
Example
setenv CLASSPATH .:/projects/bina/ch17.jar
11/11/2018
B.Ramamurthy

10. Jar your files for Prj2
Create a jar files out of all the source files (java) into a prj2.jar
Submit prj2.jar file.
One more modification: No need for print in prj2. We will do that prj3.
But save and load are needed. These can be hidden operations, that is, no need for an user interface for data saving and restoring.
11/11/2018
B.Ramamurthy

11. Summary
You can collect all the useful classes you have created into a package.
Create a CS2 package.
Use it in your future applications.
11/11/2018
B.Ramamurthy